CODEWITHSUNDEEP
javascriptgwt
CHAPa
CHAPa

Reputation: 677

GWT BOOTSTRAP - Question

Reading the GWT Bootstrap on Googles page, i have some question. (http://code.google.com/p/google-web-toolkit-doc-1-5/wiki/FAQ_WhenDoModulesLoad )

Assumptions: Most browsers will allow a maximum of two simultaneous connections for fetching resources.

The HTML Page:

<html> <body onload='alert("w00t!")'> <img src='bigImageZero.jpg'></img> <script source='externalScriptZero.js'></script> <img src='bigImageOne.jpg'></img> <img src='reallyBigImageTwo.jpg'></img> <script src='com.example.app.App.nocache.js'></script> <script src='externalScriptOne.js'></script> </body> </html>

So , the bootstrap is composed of:

  1. The HTML document is fetched and parsing begins.
  2. Begin fetching bigImageZero.jpg.
  3. Begin fetching externalScriptZero.js.
  4. bigImageZero.jpg completes (let's assume). Parsing is blocked until externalScriptZero.js is done fetching and evaluating.
  5. externalScriptZero.js completes.
  6. Begin fetching bigImageOne.jpg and reallyBigImageTwo.jpg simultaneously.
  7. bigImageOne.jpg completes (let's assume again). com.example.app.App.nocache.js begins fetching and evaluating.
  8. ...nocache.js completes, and the compiled script (...cache.js) begins fetching (this is non-blocking).
  9. ...cache.js completes. onModuleLoad() is not called yet, as we're still waiting on externalScriptOne.js to complete before the document is considered 'ready'.
  10. externalScriptOne.js completes. The document is ready, so onModuleLoad() fires.
  11. reallyBigImageTwo.jpg completes.

  12. body.onload() fires, in this case showing an alert() box.

    The question:

    how the JAVASCRIPT knows that the document is ready to begin onModuleLoad function ( step 10 ) ?

Upvotes: 3

Views: 1173

Answers (2)

necromancer
necromancer

Reputation: 24641

either nocache.js or cache.js could add an extra <script> tag immediately after the last <script> tag. this extra <script> tag would not be fetched until all previous <script> tags are fetched, parsed, and evaluated. then this <script> tag would be fetched, executed, and evaluated without waiting for any images. the evaluation of this <script> tag could call onModuleLoad() and it would not wait for any images so it would happen sooner than body.onload

this is just my theory; i could not verify it in my development server and i have not attempted to verify it on appengine.

Upvotes: 0

Hilbrand Bouwkamp
Hilbrand Bouwkamp

Reputation: 13519

From the same page:

  • <img> tags are not guaranteed to be done loading when onModuleLoad() is called.
  • <script> tags are guaranteed to be done loading when onModuleLoad() is called.

So when onModuleLoad() is executed the externalScriptOne.js is loaded, it doesn't start before all script tags are loaded.

Upvotes: 2

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